This invention relates to the technical field of adhesive compositions for medical dressings and skin-adhering devices such as ostomy products, wound dressings, and other medical products intended to be adhesively secured to skin surfaces of users. The invention is specifically concerned with such adhesive compositions that contain hydrocolloids and are capable of absorbing fluids and swelling as they do so.
Adhesive compositions containing hydrocolloids are well known, as disclosed, for example, in U.S. Pat. Nos. 5,571,080, 3,339,546, 4,192,785, 4,296,745, 4,367,732, 4,813,942, 4,231,369, 4,551,490, 4,296,745, 4,793,337, 4,738,257, 4,867,748, and 5,059,169, the disclosures of which are incorporated herein by reference. Hydrocolloids are commonly used in what is commonly referred to as hydrocolloid skin barriers. Such skin barriers normally include a water-insoluble pressure-sensitive adhesive as a continuous phase with particles of one or more hydrocolloids dispersed throughout the adhesive as a liquid-absorbing and swellable discontinuous phase.
The water-insoluble adhesive phase of commercial skin barriers typically consists of polyisobutylene, or block copolymers such as styrene-isoprene-styrene (SIS), or blends of these materials. The surface tack may be modified by the addition of tackifier components.
Whether a hydrocolloid composition is to be used as a skin barrier, for example, in conjunction with an ostomy appliance, or as a wound dressing, or as a paste, it should be capable of meeting several important requirements that often conflict with each other and, as a result, that currently available compositions cannot entirely meet. For instance, a composition that has relatively low viscosity favors adhesion to the skin, since the pressure-sensitive adhesive phase must be able to wet the skin and provide an adhesive bond. Low viscosity also allows the composition to track movement of the skin and maintain adhesion as the skin surface stretches and flexes. However, low viscosity may present its own problems. During product storage, the composition may exhibit cold flow, that is, it may flow beyond the perimeter of the product, whether it is a dressing or an ostomy skin barrier, and create problems in packaging and use. Such flow is more pronounced when such a composition is stored or otherwise exposed to elevated temperatures. In addition, compositions containing low viscosity pressure-sensitive adhesives may exhibit undesirably low cohesive strength.
Hydrocolloid-containing adhesive compositions, particularly skin barrier compositions of the type used for ostomy products, should also be moldable, since moldability promotes more secure adhesion to the skin by closely following skin contours. Moldability requires flow of the adhesive material with sufficient cohesive strength to maintain the physical integrity of the material when and while it is stretched. Additionally, the adhesive material should maintain its new shape after molding, without demonstrating “shape memory” that drives the material to return to its original shape. In general, current hydrocolloid skin barriers are deficient in moldability because they are too stiff to easily flow when stretched, have insufficient cohesive strength to maintain integrity when stretched, and/or have shape memory, tending to return to their original shape after being stretched.
Moldability, viscosity or flowability, surface tack, cohesive strength and liquid absorbency are all affected by the liquid-absorbing and swellable hydrocolloid content of a skin adhesive composition. Greater absorbency may be achieved with higher hydrocolloid content but quite often at the expense of reducing cohesive strength, surface tack, viscosity and/or moldability.
Jensen U.S. Pat. No. 5,571,080 discloses a hydrocolloid-containing adhesive composition in which filaments or fibers of polyethylene, or some other polymer compatible with the water-insoluble pressure-sensitive adhesive content (polyisobutylene) of the composition, is used to produce a three-dimensional mesh network that functions to retain the hydrocolloid particles even after they have become hydrated, thereby improving the wet integrity of the composition while at the same time maintaining its flexibility. The filaments or fibers may be formed by subjecting a polymeric film, such as a film of polyethylene having a thickness within the range of 20μ to 200μ, to a shredding operation in a rotating blade mixer, although pre-formed filaments or fibers may also be used. While such a composition may have acceptable wet integrity, it still lacks sufficient moldability and has undesirable cold flow characteristics. It is an object of this invention to provide a hydrocolloid-containing skin adhesive composition that overcomes such deficiencies.